Mar 4

Lecture Overview

• Today’s focus is on the lymphatic system and its connection to the immune system.

• Lymphatic Capillaries

  • Pick up excess fluid left behind after capillary exchange.

  • Converted fluid: from blood to lymph.

  • Permeability: High permeability due to overlapping endothelial cells (functions like mini valves).

  • Valve function: opens with increased fluid accumulation, allowing lymph uptake; closes when pressure increases.

• Lymphatic Vessels

  • Larger than capillaries; valves present to prevent backflow, partitioning vessels into chambers.

  • Functioning without a central pump through:

  • Pacemaker cells in smooth muscle aiding in contraction.

  • Skeletal muscle pump: Movement aiding lymph transport.

  • Respiratory pump: Pressure changes in thoracic cavity aiding lymph movement.

  • Proximity to arteries/veins providing external pressure waves that assist in lymph flow.

• Overall Lymphatic Circulation

  • Primary goal: return fluid to venous circulation to maintain blood volume and interstitial fluid balance.

  • Lymph travels through larger vessels, eventually merging into larger lymphatic trunks and ducts before returning to venous system via major veins (jugular, subclavian) ultimately connecting to the vena cava.

• Lymph Nodes

  • Functioning: filter lymph and involved in immune system activation by detecting pathogens.

  • Scattered throughout the body; approximately 450–500 lymph nodes.

  • Major lymphatic trunks:

  • Jugular trunk: draining lymph from head and neck.

  • Subclavian trunk: draining upper limbs, superficial thoracic wall, mammary glands.

  • Bronchomediastinal trunk: draining deep thoracic organs, thoracic wall.

  • Intestinal trunk: draining abdominal organs.

  • Lumbar trunk: draining lower limbs, pelvic organs, abdominal walls.

Structure of the Lymphatic System

• Lymphatic Ducts

  • Thoracic duct: drains most of the body; includes the right upper limb, right thorax, right side of the head.

  • Right lymphatic duct: varies among individuals; drains the right upper quadrant of the body.

• Primary Lymphatic Organs

  • Bone marrow: maturation of B lymphocytes.

  • Thymus: maturation of T lymphocytes (influenced by thymosin).

• Secondary Lymphatic Organs

  • Lymph nodes: interaction and activation of lymphocytes with pathogens.

  • Spleen: filters blood, recycles red blood cells, and enables immune surveillance.

  • Reticular tissue: composed of reticular fibers, macrophages, dendritic cells, and lymphocytes, primarily performing filtration and immune functions.

Lymphatic Tissues

• Mucosa-associated lymphoid tissue (MALT)

  • Associated with mucosal surfaces (digestive tract, respiratory tract).

  • Peyer’s patches in the intestinal area, tonsils, and appendix.

• Diffuse lymphatic tissue and lymphatic nodules

  • Diffuse lymphatic tissue: dispersed lymphocytes and macrophages that support the lymphatic nodules.

  • Lymphatic nodules: denser aggregates of lymphatic tissue typically found in lymph nodes and lymphatic organs.

Role of Lymph Nodes

• Functionality

  • Filter lymph: remove foreign substances and pathogens.

  • Organized into cortex (outer portion) and medulla (inner portion).

  • More afferent vessels than efferent; control flow and allow for meticulous filtration and immune response stimulation through prolonged exposure to filtrate.

• Clinical Significance

  • Cancer cells can accumulate and proliferate within lymph nodes, leading to metastasis and swollen lymph nodes due to concentrated immune activity.

• Swelling and Immune Response

  • Flow through lymph nodes allows interaction of lymphocytes and macrophages with pathogens and debris, facilitating responses to foreign invaders and maintaining tissue integrity before re-entry into the circulatory system.

Spleen’s Role in Blood Filtration

• Spleen Structure

  • Made up of two divisions: white pulp (lymphatic tissue involvement) and red pulp (blood filtration and recycling).

  • Functions include detecting/responding to foreign substances and recycling components of red blood cells (e.g., iron from hemoglobin).

• Blood Flow and Filtration

  • Blood flows from the splenic artery into smaller arteries in the spleen, slowing down significantly as it proceeds, allowing immune cells to examine contents.

• Emergency Blood Reservoir

  • Serves as a reserve for red blood cells, especially during physical exertion, aiding in increased blood volume

Thymus Functionality

• T Lymphocyte Maturation

  • Composed of lobules without reticular fibers, made of epithelial tissue.

  • Location for transforming immature T cells into immunocompetent cells, crucial for adaptive immune response.

• Thymosin: plays a role in T cell maturation and distribution.

• Conclusion

  • The lymphatic system functions primarily to return fluid to circulation, filter lymph and blood, and support immune responses through its structures and networks.

• Important lymphatic tissues include lymph nodes and spleen as they filter lymphatic fluid and blood, respectively.